Smudging is a problem in printing where wet ink is deposited on a medium. To overcome this problem, heated air has been used to accelerate ink drying. In the course of developing this invention it has been found that there are three factor's which control the rate of drying of a liquid deposited upon a medium, when heated air is blown across the medium surface. They are (1) the velocity of the air relative to the medium surface, (2) the temperature of the air, and (3) the relative humidity of the air. None of the earlier teachings have effectively addresses all three factors in their attempts to accelerate drying times. Each has addressed only one or two of these factors, but not all three effectively.
Previous solutions have aided drying by passing heated air over the print media. One example of this technique is taught in U.S. Pat. No. 4,340,893 by Ort, in which heated air is supplied through ports adjacent to the print head at the time of printing. In Ort, air flow must be regulated to avoid interaction with a stream of ink droplets. In another art, that of coating absorbent surfaces, U.S. Pat. No. 2,320,513 by Drummond, teaches drying of a liquid coating by passing a medium coated with liquid through a chamber in which heated air is directed onto the medium to dry the surface. It would appear from the disclosure that there is a recirculation of heated air within this chamber.
Two other U.S. Pat. Nos. 4,714,427 by Tsuruoka et al. and 4,720,727 by Yoshida, teach using heated air blown against an image surface to dry an image created on a medium surface. In each teaching, heated air is blown over a surface area without recirculation or control of velocity across a medium's surface.